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Geng H, Subramanian S, Wu L, Bu HF, Wang X, Du C, De Plaen IG, Tan XD. SARS-CoV-2 ORF8 Forms Intracellular Aggregates and Inhibits IFNγ-Induced Antiviral Gene Expression in Human Lung Epithelial Cells. Front Immunol 2021; 12:679482. [PMID: 34177923 PMCID: PMC8221109 DOI: 10.3389/fimmu.2021.679482] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2021] [Accepted: 05/17/2021] [Indexed: 01/09/2023] Open
Abstract
Infection with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19, a disease that involves significant lung tissue damage. How SARS-CoV-2 infection leads to lung injury remains elusive. The open reading frame 8 (ORF8) protein of SARS-CoV-2 (ORF8SARS-CoV-2) is a unique accessory protein, yet little is known about its cellular function. We examined the cellular distribution of ORF8SARS-CoV-2 and its role in the regulation of human lung epithelial cell proliferation and antiviral immunity. Using live imaging and immunofluorescent staining analyses, we found that ectopically expressed ORF8SARS-CoV-2 forms aggregates in the cytosol and nuclear compartments of lung epithelial cells. Using in silico bioinformatic analysis, we found that ORF8SARS-CoV-2 possesses an intrinsic aggregation characteristic at its N-terminal residues 1-18. Cell culture did not reveal any effects of ORF8SARS-CoV-2 expression on lung epithelial cell proliferation and cell cycle progression, suggesting that ORF8SARS-CoV-2 aggregates do not affect these cellular processes. Interestingly, ectopic expression of ORF8SARS-CoV-2 in lung epithelial cells suppressed basal expression of several antiviral molecules, including DHX58, ZBP1, MX1, and MX2. In addition, expression of ORF8SARS-CoV-2 attenuated the induction of antiviral molecules by IFNγ but not by IFNβ in lung epithelial cells. Taken together, ORF8SARS-CoV-2 is a unique viral accessory protein that forms aggregates when expressing in lung epithelial cells. It potently inhibits the expression of lung cellular anti-viral proteins at baseline and in response to IFNγ in lung epithelial cells, which may facilitate SARS-CoV-2 escape from the host antiviral innate immune response during early viral infection. In addition, it seems that formation of ORF8SARS-CoV-2 aggregate is independent from the viral infection. Thus, it would be interesting to examine whether any COVID-19 patients exhibit persistent ORF8 SARS-CoV-2 expression after recovering from SARS-CoV-2 infection. If so, the pathogenic effect of prolonged ORF8SARS-CoV-2 expression and its association with post-COVID symptoms warrant investigation in the future.
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Affiliation(s)
- Hua Geng
- Center for Intestinal and Liver Inflammation Research, Division of Pediatric Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Saravanan Subramanian
- Center for Intestinal and Liver Inflammation Research, Division of Pediatric Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Longtao Wu
- Section of Neurosurgery, Department of Surgery, University of Chicago, Chicago, IL, United States
| | - Heng-Fu Bu
- Center for Intestinal and Liver Inflammation Research, Division of Pediatric Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Xiao Wang
- Center for Intestinal and Liver Inflammation Research, Division of Pediatric Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Chao Du
- Center for Intestinal and Liver Inflammation Research, Division of Pediatric Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
| | - Isabelle G. De Plaen
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
- Division of Neonatology, Department of Pediatrics, Ann & Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
| | - Xiao-Di Tan
- Center for Intestinal and Liver Inflammation Research, Division of Pediatric Gastroenterology, Hepatology and Nutrition, Department of Pediatrics, Ann and Robert H. Lurie Children’s Hospital of Chicago, Chicago, IL, United States
- Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
- Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, IL, United States
- Research Service, Jesse Brown Veterans Affairs Medical Center, Chicago, IL, United States
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Lim KP, Ng LF, Liu DX. Identification of a novel cleavage activity of the first papain-like proteinase domain encoded by open reading frame 1a of the coronavirus Avian infectious bronchitis virus and characterization of the cleavage products. J Virol 2000; 74:1674-85. [PMID: 10644337 PMCID: PMC111642 DOI: 10.1128/jvi.74.4.1674-1685.2000] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/1999] [Accepted: 11/06/1999] [Indexed: 11/20/2022] Open
Abstract
The coronavirus Avian infectious bronchitis virus (IBV) employs polyprotein processing as a strategy to express its gene products. Previously we identified the first cleavage event as proteolysis at the Gly(673)-Gly(674) dipeptide bond mediated by the first papain-like proteinase domain (PLPD-1) to release an 87-kDa mature protein. In this report, we demonstrate a novel cleavage activity of PLPD-1. Expression, deletion, and mutagenesis studies showed that the product encoded between nucleotides 2548 and 8865 was further cleaved by PLPD-1 at the Gly(2265)-Gly(2266) dipeptide bond to release an N-terminal 195-kDa and a C-terminal 41-kDa cleavage product. Characterization of the cleavage activity revealed that the proteinase is active on this scissile bond when expressed in vitro in rabbit reticulocyte lysates and can act on the same substrate in trans when expressed in intact cells. Both the N- and C-terminal cleavage products were detected in virus-infected cells and were found to be physically associated. Glycosidase digestion and site-directed mutagenesis studies of the 41-kDa protein demonstrated that it is modified by N-linked glycosylation at the Asn(2313) residue encoded by nucleotides 7465 to 7467. By using a region-specific antiserum raised against the IBV sequence encoded by nucleotides 8865 to 9786, we also demonstrated that a 33-kDa protein, representing the 3C-like proteinase (3CLP), was specifically immunoprecipitated from the virus-infected cells. Site-directed mutagenesis and expression studies showed that a previously predicted cleavage site (Q(2583)-G(2584)) located within the 41-kDa protein-encoding region was not utilized by 3CLP, supporting the conclusion that the 41-kDa protein is a mature viral product.
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Affiliation(s)
- K P Lim
- Institute of Molecular Agrobiology, National University of Singapore, Singapore 117604, Singapore
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